Tuning the Acid/Base and Structural Properties of Titanate-Loaded Mesoporous Silica by Grafting of Zinc Oxide

Abstract

Mesoporous silica (SBA-15) loaded with TiO x species was synthesized by anhydrous grafting of titanium isopropoxide, and a novel procedure for the preparation of ZnO x /SBA-15 materials by grafting of Zn(acac) 2 was explored.The TiO x /SBA-15 and ZnO x /SBA-15 materials as well as subsequently prepared bifunctional ZnO x -and TiO x -containing SBA-15 materials were characterized in depth by combining N 2 physisorption measurements, UV−vis, X-ray photoelectron and Xray absorption spectroscopy, and CO 2 and NH 3 temperatureprogrammed desorption experiments. The characterization results confirmed a close proximity of ZnO x and TiO x in the subsequently grafted materials. Because of strong interactions between the Zn precursor and the SiO 2 surface, the order of the ZnO x and TiO x grafting steps affected the amount of Ti−O−Zn bonds formed in the materials. When ZnO x is present in SBA-15, subsequently grafted TiO x is higher coordinated and more Ti−O−Zn bonds are formed compared to SBA-15 in which TiO x was introduced first, indicating strong interactions between the Ti precursor and ZnO x . While all TiO x and ZnO x -containing samples exhibit a large amount of acidic sites, ZnO x present as isolated species or small clusters in SBA-15 significantly improves the CO 2 adsorption capacity by introducing basic sites. In the subsequently grafted samples the amount of acidic and basic sites is found to be unaffected by the order in which the two transition metals are introduced.

Facile and Versatile Sol–Gel Strategy for the Preparation of a High-Loaded ZnO/SiO2 Adsorbent for Room-Temperature H2S Removal

“…The latter (1024.7 eV) showed a positive shift (3.6 eV) in comparison with the former (1021.1 eV), indicating a decrease in the outer electron cloud density of Zn 2+ . Such behavior was observed by Tkachenko et al and Mei et al, and they ascribed the peak with the higher binding energy to ZnO x . , However, no further evidence in this study confirmed the formation of a ZnO x species. According to the FT-IR results showed in Figure a, this peak was confirmed to be related to the monodentate ZnCO 3 species.…”

“…Such behavior was observed by Tkachenko et al and Mei et al, and they ascribed the peak with the higher binding energy to ZnO x . 39,40 However, no further evidence in this study confirmed the formation of a ZnO x species. According to the FT-IR results showed in Figure 4a, this peak was confirmed to be related to the monodentate ZnCO 3 species.…”

Synthesis and Characterization of Platinum Nanoparticle Catalysts Capped with Isolated Zinc Species in SBA-15 cChannels: The Wall Effect

“…Figure4B shows that on increasing the zinc content in the Pt-Zn/SBA-15 series, the white line intensity decreases and the peak splits into a strong doublet which agrees with the results which have been previously reported by Mei et al who attributed the formation of [ZnO4] 6on silica surfaces. 37 The similarity in lattice and coordination number matching with internal silica surface appears to offer a strong directing role to bind Zn ions preferentially from the mixture of Pt and Zn precursors. Analysis of the Zn K edge EXAFS demonstrates there is no long range ordered structure present in the local coordination environment of the Zn atoms.…”

Photocatalytic Methanol Oxidation by Supported Vanadium Oxide Species: Influence of Support and Degree of Oligomerization

“…For low vanadium oxide (VO x ) loadings (up to about 1 V nm –2 ), the specific surface area (SSA) of the catalysts is hardly affected by the VO x layer, whereas higher loadings lead to a decrease of the SSA. This decrease in SSA might be attributed to the clogging of small pores of the support by the grafted or impregnated metal oxide species …”